1. Field of the Invention
The present invention relates to a light-receiving semiconductor device, an optical pickup device, and an optical disk device. In particular, the invention relates to a light-receiving semiconductor device having different receiving sensitivities.
2. Description of Related Art
Up to now, a CD-ROM (Compact Disk Read Only Memory) or the like has been used as a recording medium typified by an optical disk. In recent years, various kinds of recording media have been developed along with an increase in recording capacity of electronic data. For example, a DVD-ROM (Digital Versatile Disk Read Only Memory) having a large recording capacity has been used in place of existing CD-ROMs. An optical pickup for reading data recorded on such an optical disk has been developed.
In the optical pickup used in CD/DVD (Compact Disk/Digital Versatile Disk) and the like, laser light is irradiated to the disk to write/read information. As for the write/read processing, laser light power is large during writing data and is small during reading data. Accordingly, a light receiving element that receives laser light for writing/reading data should detect both of strong light and weak light with high accuracy. Meanwhile, high-speed response is required of the light receiving element along with an increase in recording speed.
Japanese Unexamined Patent Application Publication No. 2001-209959 discloses an example of the optical pickup circuit. In the optical pickup circuit, a photocurrent from one light receiving element is supplied to an amplifier capable of switching an amplification factor. The amplifier switches its amplification factor to a small amplification factor at the time of detecting strong light and to a large amplification factor at the time of detecting weak light.
The above optical pickup circuit switches a gain to a low gain when receiving strong light and to a high gain when receiving weak light to thereby detect a signal without decreasing an S/N ratio.
As shown in FIG. 8, in the case of switching an amplification factor of the amplifier, an amplification factor of an operational amplifier for amplifying a signal is inversely proportional to a frequency band, resulting in a problem in that high-frequency response characteristic reduces as the large amplification factor is increased for detecting a signal of weak light.
In addition, Japanese Unexamined Patent Application Publication No. 2000-258244 discloses an in-vehicle optical sensor that detects weak current. In the optical sensor, a light-receiving surface of a light receiving element is split, and a car air conditioner is controlled in accordance with a received light amount of each light receiving region.
The conventional optical pickup circuit detects strong light and weak light during reading/writing data in this way and thus has a problem in that both of high detection accuracy relative to an incident light intensity and high-speed response characteristic are difficult to realize.